In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce the pressure of a fluid. Adjustable flow restriction devices such as flow control valves and fluid regulators and other fixed fluid restriction devices such as diffusers, silencers, and other back pressure devices are utilized for this task. The purpose of the fluid control valve and/or other fluid restricting device in a given application may be to control flow rate or other process variables, but the restriction induces a pressure reduction inherently as a by-product of its flow control function.
Currently there is available an assembly of a plurality of stacked disks forming a fluid pressure reduction device fused together in a brazing process with additional mechanical fasteners added if desired to securely maintain the stacked disks assembled. As an example, in U.S. Pat. No. 6,026,859, assigned to the same assignee as herein, a plurality of stacked disks include alternating flow disks and plenum disks. Respective cage ends are provided on opposite ends of the stacked disks. One of the cage ends includes a series of threaded bores and the opposite cage end includes a corresponding number of countersunk bores. A corresponding number of holes are drilled, cut or punched through each disk so that in the assembled stacked disks configuration, each disk hole can be aligned with a respective threaded bore in one cage end and with a respective countersunk bore in the opposite cage end. In the final assembly, a threaded bolt is inserted through the one cage end and through the disks to threadably engage the threaded bore in the opposite cage end.
In the manufacturing process for this stacked disk assembly, each individual disk and the cage ends are coated with a nickel plating. The nickel plated disks and the cage ends are assembled into a stack which is placed in a fixture and subjected to a suitable temperature in an oven during a brazing process to fuse the individual plated disks to each other as well as to the opposite cage ends.
Problems have been encountered in thereafter attempting to threadably engage the threaded bolt with the threaded bore in the cage end due to the nickel in the brazing process being deposited into the threads of the threaded bore. Various attempts have been made to prevent the nickel from being deposited onto the threads in the cage end threaded bores, all of which attempts have met with limited success. Thus, despite various efforts the final assembly problem in trying to provide a mechanical fastening of the stacked disks still exits.
Other problems encountered are due for instance to distortion in the threads caused by the high temperatures in the brazing oven. Thread distortion may cause increased difficulty in assembly, overtorqueing of the threaded bolt, and insufficient bolt load.